Cognitive Neuroscience Lecture 9: Face and Scene Recognition
L9: Face and Scene Recognition '' The dress: color constancy Specialization in ventral occipital cortex - Sub-regions specialized for particular visual categories o E.g. faces, places, words, bodies, other ppl’s thoughts Face vs. Scene Area - Fusiform Face Area (FFA): '''right fusiform gyrus': Faces>scenes - Parahippocampal place area (PPA): Scenes>faces - PPA is superior and medial to FFA Fusiform & Parahippocampal gyrus: WHICH OF THESE DO WE NEED TO KNOW? - Fusiform: lateralish; right ffa. - Parahippocampal: medialish - “If neuroimaging is the answer, what is the question?” - It’s not good enough to just put a bunch of people thru an fMRI during a task and then retroactively assign meaning to the observed activated parts - You should have targeted question about targeted area Useful types of imaging studies: - Characterization of a single neuron’s responses o What happens with one vs another - fMRI study on Face o Kanwisher FFA paper most successful empirical fMRI paper (not method/survey paper) o Studied macaque temporal lobe § Showed cells that specifically responded to faces, not scrambled faces or other obj o Humans lose ability to recognize faces but not other objs § Prosopagnosia o Human fusiform gyrus was implicated in face in earlier PET studies § They gave it a catchy name - Background: fusiform gyrus activated for faces, but control stim weren’t controlled for - Question: is processing of faces distinct from processing of obj when other confounds are eliminated? 1. Face localizer scans a. Faces vs objs. b. Block design (faces, fixation, objs, fixation) c. Higher during face blocks d. Subtraction method: faces – objs = face specific area 2. ID ROI in each individual a. Is there a place in each individual that responds more to faces than obj? b. Is this place the same in all subjects? c. yes in 12/15 subjects 3. Test alternative hyps in ROIs: low level diffs, exemplars, animate? a. Could be that FFA is for any low-level feature differences (overall contrast, luminance, shape?) i. If FFA is truly face selective, it should respond more to faces than scrambled faces ii. This would mean it’s not responding just to anything with differences in luminance/contrast iii. Block design of Scrambled vs Intact faces shows it does b. Could also be that FFA is for anything that is exemplar of a category i. Faces are exemplars of a face category but there are multiple basic-level category of objects ii. If FFA is truly face selective, it should respond more to faces than houses even though individual houses, like faces, are exemplars within a category of similar objs c. Could be that FFA is for anything animate i. If FFA is truly face selective, it should respond more to faces than hands ii. It does (block face vs. hands) iii. What if it’s just for anything that requires more attention? iv. When 1 back task forced attention to hands, it still didn’t light up for handsà not attention Conclusions - A part of right fusiform gyrus is preferentially active during face viewing - “faces are special”à not just another stim Why was this paper so successful? - Discovered area that became hugely studied - Goal was not just localization but a deeper understanding of brain activation patterns - Theoretically driven o “are faces special” o Relates well to other lit - Unambiguous o Good controls - Beginning of controversy o Category specificity o Nature vs. nurture At what level does the brain represent categories? - Many more questions…viewpoint, ID vs appearance, facial expression, facial parts, “special” 'fMRI adaptation: '''what counts as the same in the brain? - If you show a stim twice in a row, you get a reduced response the second time - fMRI adaptation/attenuation o “different” trial: high response both times o “same” trial: low response second time o When you do it a second time, neurons are tired and you get less activity if you do the same thing twice (same neurons activated) - Why is adaptation useful? o Now we can ask what it takes for stim to be considered “Same” o E.g. viewpoint - Repeated individual, diff viewpoint o Possibility 1: '''viewpoint specificity '(Area codes face as diff when viewpt changes; high response) o Possibility 2: 'viewpoint invariance '(area codes face as same despite viewpt change) - Results o Identical Faces/ objects - PPA: right above cerebellum, right below ventricles - - Parahippocampal gyrus: below the hippocampus, left side - Fusiform gyrus: lateral - PPA: Empty room, furnished room, lego room, fractured room as long as spatial layout intact, houses&landmark, geometry o Not furniture - Perhaps PPA computes features that describe ''geometry ''of scene o Nope; real scenes give higher % signal change than scrambled scenes, rooms, objs - Viewpoint invariance or specificity in PPA? Ask using fMRI adaptation paradigm o Obj change, viewpoint change, place change o Identical